At electric powered lifting trucks with forks of the type warehouse trucks, there is utilized large and heavy batteries for allowing long working cycle times between recharging of the battery. The utilization of the batteries can be divided into two different operation cases. The battery can be charged on board the truck, or the battery can removed from the truck and charged. In the latter case there is provided several batteries that can replace the battery on charge.
In the case with batteries to be charged on board of the truck, the battery is connected in situ in the truck to a charging station. The truck is inoperable during the charging period, but at the same time battery switches are avoided and it is thereby possible to save the cost for extra batteries, as well as the management of these. When connecting, the contact at the battery is detached from the circuit that leads to the consuming items in the truck. Thereafter the battery is connected to a charge cable that leads to a battery charger, as an alternative a charger can be present on the truck and in that case the cable is connected to a power supply.
When the battery is to be charged, the connector of the battery also named charging glove, is disconnected from the corresponding contact in the truck and instead connected to a charging socket on the charging station. The charging glove in trucks is of the slide on type. I.e. a male contact and a female contact are united and a lock applies to keep the contact in position, during the charging process, and this also when connecting consumers and the battery. The force that is needed to bring the two elements together is required in order to achieve contact, in particular when large currents are dealt with in the order of 100 to 500 Amperes. As disconnection and connection of the charging glove is done daily or sometimes several times a day, wear of the charging glove is inevitable. Thus it has not traditionally been of interest to introduce something else than the simplest shape of a charging glove as this has to be exchanged on a regular basis.
The batteries of electrically powered trucks have an energy density that is measured in hundreds of Ampere hours. Batteries with less than 100 Ampere hours are non-existent. Thus equipment for batteries with lower energy content is not considered a possibility for batteries for electrically powered trucks. Batteries can be charged in two ways. On one hand the battery can be charged on board of the truck or the discharged battery can be replaced with a fully charged battery and the discharged battery is charged separated from the truck. The latter is common when the truck is operated in shifts, as the recharging of the battery takes approximately a shift.
When charging the battery on board, the battery is connected to the connector with a cable. The connector has two contacts one for positive and one for negative, exactly as the output current from the battery. The cable usually has a length so that it at disconnection from the consumer can be connected to the charging station. The length of the cable is thus provided such that the connection of the battery can be performed outside the line of periphery of the truck. With periphery line is intended a horizontal circumference that follows the contour of the truck at different levels. In the forward direction the periphery line is limited by the lift forks, the sides by the truck body itself or as an alternative by a broader fork sledge. When the cable is connected to the consumers there is in other words an excess in length of the cable. This must be dealt with, primarily as the outgoing cable from the battery is not secured with a fuse. To roll up the cable is difficult due to the thick dimension. If the operator handles the cable wrongly and allows it to hang outside the truck body a security risk occurs. A stressed operator can thus instead of stowing the cable under for example a hatch, neglect to do this. It is thus the length of the cable that allows for this loop to be hanging out.
The connection of the cable is in general positioned close to the battery, which is in the vicinity of the gravity centre of the truck. In the vicinity of the gravity centre is generally also positioned for example the hoisting device such as the lifting mast. It is easy to understand that if the cable thus is clamped for example in the mast, the battery is short circuited, which not only destroys the battery but also can lead to fire or worse injuries to the personnel that is operating the truck. To solve this there are different solutions. One of these involves that the two poled cable and the two pole connection contact are always positioned under a hatch that always is to be closed during operation. Another simpler solution is that one has a fixed connection contact on the truck without a loose cable. To then achieve connection and disconnection of the consumers a three pole contact is introduced on the truck. To this contact is in operation of the truck two of the poles connected with each other with a so called operation clamp, to thereby connect the battery to the consumers.
At charging, the operation clamp is removed and instead the charging cable is connected to two of the three poles, one of which is common with the connection of the operation clamp. The operation clamp and the charging cable are connected to the battery at breast height of an operator, when this system is used in on large trucks, such as reach trucks and very narrow aisle trucks. A simple and well operating operation clamp has a handle with two pins that can connect the circuit to the consumers but leave the third hole free. From the asymmetry for an operation clamp and a charging contact it can be understood that a swivel effect occurs when connecting two pins towards three holes. The swivel effect augments the push force. When at breast height when connecting on a larger warehouse truck, the push force or pull force does not exceed the force a general operator can achieve, thus the operation clamp can be made in the simplest possible way.
The warehouse trucks is more and more used as effectively as possible, i.e. the operating time at each hour of performed work increases more and more, as more goods is to be handled. To manage this rate it is required more and more energy to the consumers per time unit in warehouse of trucks today. Not at the least for performing higher lifts and higher transport velocities than before. With higher transport velocity is also added the ability to increase the warehouse area and thus longer transport distances are added each shift. All these measures provides for an increased need to charge more often has been added, the warehouse truck turns over more energy and needs power supply more often and in larger amount. In connection with this it has been found that the push force and the disconnection force for the charging contact has an increased importance to the ergonomic when using warehouse trucks. I.e. with an increased frequency of charging a need arises for simplifying disconnection of the operation clamp and connection of the charging contact by improved accessibility. For example it is a desire to avoid the said hatch without inducing a problem with cable breaks due to loosely hanging cables.
At an increased charging frequency a problem also arises when a stressed operator does not disconnect the charging process before the charging contact is disconnected. To solve this, a charger that can automatically disconnect the current has been introduced. However the disconnection does not occur fast enough if the operator snatches away the charging contact. The on-going charging process will then have no time to be aborted by the charger. This can give rise to formation of sparks and disturbance of the function of the battery.